Regional brain studies on indoles and tyrosine in Mongolian gerbils during nutrition with artificial mixtures high in branched chain amino acids compared to a protein rich diet.

Up till now evidence is lacking regarding the regional distribution of indoles, like tryptophan (TRP), serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) as well as tyrosine (TYR) in the brains of Mongolian gerbils. Therefore using a microdissection technique and pooling regional brain samples, it can be shown that there is a regional distribution of 5-HT and 5-HIAA in the brain of Mongloian gerbils which is highest in the raphe + reticular formation system followed by the rest of the brainstem and lenticular nuclei. A longterm fast (22 hours) increases TRP and 5-HIAA but not 5-HT, indicating an increase in the turnover rate of 5-HT. Brain TYR and TRP are only slightly increased after a protein rich diet, whereas 5-HT and 5-HIAA are not changed. Artificial nutrition with amino acid mixtures highly concentrated with branched chain amino acids lead to a decrease of TYR and TRP as well as 5-HT and 5-HIAA. Competing amino acid as well as inhibition of 5-HT synthesis is suggested to be responsible for these effects. Mongolian gerbils show higher brain values of TRP and lower ones of TYR in comparison with other species of mice. In peripheral organs, specially in the liver and lung, similar effects are observable. However, the changes are only mild in comparison to that observed in the brain. Moreover, TYR and TRP are significantly increased in peripheral organs after a protein rich diet.